1. Field of the Invention
The invention discloses new drilling fluids and invert drilling muds based thereon, which are distinguished by high ecological acceptability and at the same time good storage and application properties. An important area of application for the new drilling fluid systems is in off-shore wells for the development of petroleum and/or natural gas deposits, the aim of the invention being particularly to make available industrially usable drilling fluids with high ecological acceptability. The use of the new drilling fluid systems has particular significance in the marine environment, but is not limited thereto. The new mud systems can be put to quite general use even in land-based drilling, for example, in geothermal wells, water bore-holes, in the drilling of geoscientific bores and in drilling for the mining industry. Here too it is essentially true that associated ecotoxic problems are substantially simplified by the ester-based drilling-oil fluids selected according to the invention.
2. Discussion of Related Art
Oil-base drilling fluids are generally used in the form of so-called invert-emulsion muds, which consist of a three-phase system: oil, water and finely particulate solids. These are preparations of the W/O-emulsion type, i.e. the aqueous phase is distributed as a heterogeneous fine dispersion in the continuous oil phase. A number of additives can be used to stabilize the system as a whole and to confer on it the desired application properties, particularly emulsifiers or emulsifier systems, weighting agents, fluid-loss additives, alkali reserves, viscosity regulators and the like. For details, refer, e.g., to the publication by P. A. Boyd et al. "New Base Oil Used in Low-Toxicity Oil Muds" Journal of Petroleum Technology, 1985, 137 to 142, and R. B. Bennett, "New Drilling Fluid Technology--Mineral Oil Mud" Journal of Petroleum Technology, 1984, 975 to 981 and the literature cited therein.
The importance of ester-based oil phases in reducing the problems created by such oil-base muds has been recognized for some time in the relevant field of technology. For example, U.S. Pat. Nos. 4,374,737 and 4,481,121 disclose oil-base drilling fluids in which non-polluting oils are to be used. The following are of equal value as the non-polluting oils--mineral oil fractions which are free from aromatic hydrocarbons, and vegetable oils, such as peanut oil, soybean oil, linseed oil, corn oil, rice oil or even oils of animal origin, such as whale oil. These named ester oils of vegetable and animal origin are all, without exception, triglycerides of natural fatty acids, which are known to be of high environment acceptability, and are clearly superior ecologically to hydrocarbon fractions--even when these do not contain aromatic hydrocarbons.
Interestingly enough, however, not one of the examples in the above U.S. patent specifications describes the use of such natural ester oils in invert-drilling fluids of this type. In every case, mineral oil fractions are used as the continuous oil phase. Oils of vegetable and/or animal origin are not considered for practical reasons. The rheological properties of such oil phases cannot be controlled over the wide temperature range generally required in practice, from 0.degree. to 5.degree. C. on the one hand, up to 250.degree. C. on the other.